Method of manufacturing a plastic insulated wire

ABSTRACT

THIS INVENTION DEALS WITH A METHOD OF MANUFACTURING PLASTIC INSULATED WIRES IN WHICH THE INSULATING TAPE OF PLASTIC MATERIAL IS CONTINUOUSLY MOLDED TO LONGITUDINALLY APPLY IT TO AN ADVANCING INNER CONDUCTOR IN THE SUCCEEDING STEP OF THE PROCESS. A LENGTH OF A FORMING TAPE IS TEMPORARILY APPLIED IN THE PROCESS TO THE PLASTIC INSULATING TAPE ALONG ITS LENGTH TO SERVE AS A FORMING MEMBER FOR THE PLASTIC INSULATING TAPE.

Feb 16, 1971 AKIRA NAGO 3,563,820

METHOD OF MANUFACTURING A PLASTIC INSULATED WIRE Filed Aug. 20, 1968 2 Sheets-Sheet 1 Feb 16,1971 AK. M60 3,563,820

METHOD OF MANUFACTURING A PLASTIC INSULATED WIRE Filed Aug. 20, 1968 2 Sheets-Sheet 2 United States Patent 3,563,820 METHOD OF MANUFACTURING A PLASTIC INSULATED WIRE Akira Nago, Funabashi-shi, Japan, assignor to The Tujikura Cable Works Limited, Tokyo, Japan, a corporation of Japan Filed Aug. 20, 1968, Ser. No. 753,943 Int. Cl. H01b 13/06 US. Cl. 156-54 5 Claims ABSTRACT OF THE DISCLOSURE This invention deals with a method of manufacturing plastic insulated wires in which the insulating tape of plastic material is continuously molded to longitudinally apply it to an advancing inner conductor in the succeeding step of the process. A length of a forming tape is temporarily applied in the process to the plastic insulating tape along its length to serve as a forming member for the plastic insulating tape.

This invention relates to a method of manufacturing plastic insulated wires, more specifically to a method of manufacturing the insulated wires or cores suitable for coaxial cables in which the inner conductors are surrounded by coatings made of plastic insulating material.

In general, the coaxial cable comprises an inner conductor, an insulator surrounding the inner conductor and an outer conductor coaxially arranged to the inner conductor through insulating material interposed therebetween. As insulators, various plastic materials, such as polyethylene, forming polystyrene and the like may be used for the coaxial cores. 'In one of manufacturing processes of such type of the coaxial cores, the plastic tape is provided to the inner conductor along its length and is then shaped tosurround the inner conductor therein. According to such a process, plastic material disposed around the inner conductor and the outer conductor are simultaneously formed in which case the inner surface of the outer conductor serves as a forming means.

Accordingly, in such a manufacturing process, the outer conductor to be used is limited to flat tape of copper. In some cases, however, the corrugated tube of metal such as copper, aluminum or the like and the metal braid is used as an outer conductor for coaxial cable. For the manufacture of such a coaxial cable, it is impossible to apply such forming method that plastic tape is longitudinally applied and the outer conductor is utilized as a forming means as set forth above. In order to enable to manufacture the coaxial cable with any desired form of outer conductor, it is desirable to perform only an insulated core and thereafter to provide the outer conductor thereto in another step.

On the other hand, the tape produced by a mold has properties of deformation such as contraction with the lapse of time due to the internal residual strain occurred at the time when the tape was produced. Therefore, in case that plastic tape which is applied around the inner conductor is performed separately, each lot of the plastic tape, for example, each roll of the tape wound in each reel has different degrees of deformations per reel. When the coaxial cable is manufactured by using such plastic tape, the resultant coaxial cable has variations in shape of the insulating separator of each lot, and therefore such variations in shape of the insulating separator have a bad effect on electrical characteristics of the resulted cable. In order to prevent the shape of the plastic tape from varying with the lapse of time, it is desirable to continuously mold the plastic tape in the desired form in succession to the consecutive step of longitudinally applying the plastic tape to the inner conductor.

Further, from viewpoint of electrical characteristics the coaxial cable requires precision of the inside diameter of the outer conductor, that is, the outside diameter of the insulating separator, and therefore when the supply of plastic tape is interrupted during the manufacture of the cable, it is difficult to bond the tapes in the end to end relationship without injuring such precision as set forth above while the manufacturing machine is operating continuously. Thus, it is desired that the plastic tape should be supplied Without interruption incident to the feeding of the inner conductor.

Therefore, an object of the invention is to provide a method of manufacturing plastic insulated wires which, on the economical basis, have uniform electrical characteristics along their length with less variations in the outside diameter of the insulating separator.

In accordance with an aspect of the present invention, plastic materials such as polyethylene, polystyrene etc. are extruded and molded in the tape form, and the resulted tape is longitudinally supplied to advancing conductor to perform heat forming of the tape around the conductor. Thus, the plastic tape can be continuously covered around the center conductor without irregularities, thereby to improve electrical characteristics.

In accordance with an important aspect of the present invention, when the plastic insulating tape is heat-formed along the length of the center conductor, a flexible forming tape is longitudinally fed outside of the plastic tape to serve as a forming aid member so that heat forming process of plastic insulating tape is advantageously controlled, with the result that variations in the outside diameter of the insulating separator is prevented and the irregularities of electrical characteristics are removed.

In accordance with another aspect of the present invention, the low cost forming tape can be employed and peeled off with ease from the plastic coating of the wire, and therefore the expected wires can be easily produced on the economical basis.

The objects, aspects and advantages will be understood by considering the following description in conjunction with the attached drawing.

In the drawing:

FIG. 1 shows cross-section of the insulated wire produced in accordance with the method of the present invention,

FIG. 2 is a schematic diagram showing a preferred embodiment of an apparatus embodying the method of the present invention,

FIG. 3 is a perspective view of the plastic insulating material extruded from an extruder which is used in practising the method of the present invention,

FIG. 4 is a plane view of a heat forming device to be used in the apparatus of FIG. 2, and

FIGS. 5A, 5B, 5C, and 5D are respectively sectional views taken along the lines 5A5A, 5B5B, 5C5C and 5D5D of FIG. 4.

Referring to FIG. 1, there is shown cross sectional view of the insulated wire manufactured in accordance with the method of the present invention. The insulated wire comprises a center conductor A and a plastic insulating tape B, the plastic insulating tape surrounding the center conductor. In the illustrated embodiment, the plastic insulating tape is of polyethylene material and have a plurality of protrusions in one side thereof as described in detail hereinafter. When the both edges of the plastic insulating tape are butt welded at the junction portion (C), the head portions of the protrusions position the center conductor in place in contact with the center conductor.

FIG. 2 shows schematic diagram of an apparatus for use in the practise of the method in accordance with the present invention. In FIG. 2, polyethylene insulating tape is extruded by an extruder 1. This extruder may be any type of conventional ones. The polyethylene insulating tape extruded from the extruder 1 enters into a pair of molding rolls 2 to mold the polyethylene tape into the desired form. In the illustrated embodiment, the polyethylene tape has on both side edges fusion allowances a which are thinner than the main portion and has on one side a plurality of protrusions a a arranged substantially uniform, as shown in FIG. 3. Arrangement of the protrusions may be taken in any desired form. In the illustrated embodiment, four protrusions are arranged in a row at regular intervals on the one surface of the polyethylene tape perpendicular to its length, and each row of four protrusions is arranged in a column to alternate with adjacent row of four protrusions.

The undesired portions of the polyethylene insulating tape are cut off by a cutter 3 to shape it into the predetermined form. The insulating tape is extracted by a capstan 4 and guided through a pair of dancer rolls 5 and 5 to guide roll 6. The advancing polyethylene insulating tape B guided by the guide roll is fed, at a heat forming devices, to the center conductor A along its length which is supplied from a supply device 8 through a pair of conductor guide rolls 9 and 9'.

In accordance with an aspect of the present invention, the forming tape is supplied from a feed device 10 through a pair of guide rolls 11 and 12 and is advanced along the polyethylene tape B. In heat forming, the forming tape is supplied along the plastic insulating tape. The forming tape which is applied around the insulating tape may be selected from any suitable materials. In one embodiment, one kind of material such as cellophane is employed which is easily peeled off from the plastic insulating material. In another embodiment, normal paper, metallized paper or the like as a forming tape are employed and coated on one surface with parting agent such as silicone oil, the coated surface of the forming tape is in contact with the plastic insulating material longitudinally. A parting agent coating unit 13 is provided between the guide rolls 11 and 12 for applying the parting agent to the forming tape fed from the feed device 10. In further another embodiment, for the forming tape, an adhering combination of paper tape and cellophane tape is employed. Since the cellophane tape does not adhere to the plastic insulating tape, even in the fused condition, in nature, the cellophane surface of the combination is in contact with the plastic insulating tape when it is shaped in the cylindrical form in cross section. This case does not require a parting agent and in addition the paper tape can advantageously stand substantial tension during manufacturing the insulating wire.

The forming tape may be of any other materials and plays an important role to prevent the plastic insulating material from deviating or deforming from the regularities. On the other hand, since it is common that the forming tape is thrown away after once usage and is not used repeatedly, the shaping tape is advantageously made of materials as set forth hereinbefore.

The polyethylene insulating tape B as well as the forming tape which are longitudinally applied to the travelling center conductor A are heated by the heat forming device 7 to the temperature within the range of C. to C. to form them into the cylindrical form and fed from the heat forming device to a fusion-contacting apparatus which comprises a slotted guide 14 and a hot blowing unit 15.

One example of the heat forming device 7 is shown in FIG. 4. On the inner surface of the heat forming device, polytetrafluoroethylene referred to as trade name Teflon is baked. As shown in FIG. 4, the device 7 consists of a guide section, a forming section, and a die section. Cross sectional views taken along the dotted lines SA-SA, SB-SB, 5C-5C and 5D5D are shown in FIGS. 5A, 5B, 5C and 5D respectively.

At the guide section in FIG. 5A, the center conductor A, the plastic insulating tape B and the shaping tape D 4 are arranged in superimposed position and supplied into the forming section. The forming section shown in FIGS. 58 and 5C has an inner wall having successively narrowing circular cross section, whereby the supplied members are formed so as to embrace the center conductor A.

The die section shown in FIG. 5D has a hole of circular sec ion, the hole being joined with the outlet opening of the forming section. Accordingly, during passing of the supplied members through the die section, the members are subjected to heating by the heating device (not shown) and the plastic insulating tape is transformed to a tube shape. The plastic insulating tape B in the tubular form surrounding the center conductor A is advanced through a die 16 for outer diameter adjusting and is guided so that the fusion allowance is positioned in the slot (not shown) of the slotted guide 14, and the heating fluid is blowed into the slot to butt weld the fusion allowances of the insulating tape B. The heating fluid may be hot air, vapor or the like.

In the alternative embodiment which is not shown in the drawing, the plastic insulating tape may be butt welded at the fusion allowances a thereof in the heat forming device 7 in which case the slotted guide and hence the hot blowing unit 15 are not required for the purpose of butt welding.

The insulated wire formed in such a manner as mentioned above is fed to a forced cooling system 17 to cool the wire. Then the insulated wire is passed through a capacity measuring unit 18 to measure a electrostatic capacity of the wire. In accordance with the measured result by the unit 18, the insulated wire is always controlled to provide the predetermined values by adjusting extracting speed of the capstan 19, the temperature within the slotted guide 14 and so on. Although there is not shown, the

' forming tape D is peeled off from the plastic insulated wire at the front or rear of the capacity measuring unit 18. The insulated wire is passed through a capstan 19 and wound by a take-up motion 20.

It is noted that the present invention has been described in connection with one embodiment but this embodiment is only illustrative. It may be easily understood that the present invention can be modified and improved by one skilled in the art without departing the spirit and the scope of the present invention.

What is claimed is:

1. A method of manufacturing a plastic insulated wire characterized in that the method comprises the steps of applying a plastic tape to an advancing conductor along .its length while the plastic tape is being produced by an extruder, applying a forming tape to the outside of the plastic tape along its length, applying a plastic coating around the conductor by means of a heat forming device, and peeling otf the forming tape embraced around the plastic coating.

2. A method of manufacturing a plastic insulated wire according to claim 1, characterized by the steps of applying a parting agent to the forming tape, and then supplying it to the heat forming device.

3. A method of manufacturing a plastic insulated wire according to claim 2, characterized in that the forming tape is made of paper.

4. A method of manufacturing a plastic insulated wire according to claim 1, characterized in that the forming tape is made of cellophane.

5. A method of manufacturing a plastic insulated wire according to claim 1, wherein the forming tape consists of paper adhering to cellophane, the application of the forming tape bringing the cellophane into contact with the outside of the plastic tape along its length.

References Cited UNITED STATES PATENTS 3,341,385 9/1967 Nago 156-54 VERLIN R. PENDEGRASS, Primary Examiner 

